Process for the preparation of aqueous suspensions of anionic colloidal silica having a neutral ph and applications thereof

ABSTRACT

The instant invention relates to a process for the preparation of an aqueous suspension of anionic colloidal silica having a neutral pH which is stable over time and comprises individualized particles of colloidal silica which are not bound to one another by siloxane bonds. The instant suspensions show high storage stability and are particularly useful for the clarification of beer, for the preparation of cosmetic formulations, for the production of ink for printers, for paints and for anticorrosive treatments.

[0001] The present invention relates to a process for the preparation ofaqueous suspensions of anionic colloidal silica having a neutral pH andthe applications thereof.

[0002] EP-A-0.878.838 discloses that aqueous suspensions of colloidalsilica having a neutral pH may be obtained either by neutralization ofalkaline silica sols by an acid solution (solution of nitric,hydrochloric or sulfuric acid), or by neutralization of acid silica solsby a basic solution (solution of potash or ammonia). However, dependingon the operating conditions, a limited stability over time of thecolloidal suspensions obtained is most often obtained, which limitstheir commercial development, particularly for colloidal suspensionshaving a high specific surface, which are the least stable.

[0003] The applicant discovered, with surprise, that by mixing an acidsilica sol with a basic silica sol, a neutral silica sol was obtainedunder remarkable conditions and that the sol obtained exhibitedremarkable properties, notably a remarkable storage stability over time.

[0004] Moreover, by means of the process according to the invention, itis possible to prepare suspensions of anionic colloidal silica having aneutral pH and having a high silica content of at least 5% by weight oreven up to 25 to 30% by weight and optionally more than 30% by weight,whilst retaining excellent stability over time, and this in particularfor suspensions of individualized particles of colloidal silica notbound to one another by siloxane bonds.

[0005] For this reason, the present invention provides a process for thepreparation of an aqueous suspension of anionic colloidal silica havinga neutral pH (between pH 6 and 8), which is stable over time andcomprises individualized particles of colloidal silica which are notbound to one another by siloxane bonds, characterized in that an aqueoussuspension of anionic colloidal silica comprising individualizedparticles of colloidal silica which are not bound to one another bysiloxane bonds and having a basic pH is mixed with an aqueous suspensionof anionic colloidal silica comprising individualized particles ofcolloidal silica which are not bound to one another by siloxane bondsand having an acid pH.

[0006] The particles of the suspensions of anionic colloidal silicahaving a neutral pH are preferably individualized particles of colloidalsilica which are not bound to one another by siloxane bonds, havingadvantageously a particle diameter in the range from 4 nm to 150 nm,notably from 4 nm to 100 nm, preferably from 4 nm to 50 nm, particularlyfrom 5 nm to 50 nm and more particularly from 9 nm to 50 nm.

[0007] The particles of silica used in the invention advantageously havea specific surface in the range from 20 m²/g to 700 m²/g.

[0008] The present invention provides, particularly, a process for thepreparation of an aqueous suspension of anionic colloidal silica havinga neutral pH (between pH 6 and 8) which is stable over time andcomprising individualized particles of colloidal silica which are notbound to one another by siloxane bonds, wherein an aqueous suspension ofanionic colloidal silica having a pH in the range from 8.5 to 11, aspecific surface in the range from 20 m²/g to 700 m²/g, a particlediameter in the range from 4 nm to 150 nm and having a percentage ofsilica greater than or equal to 5% by weight, is reacted with an aqueoussuspension of anionic colloidal silica having a pH in the range from 2to 3.5, a specific surface in the range from 20 m²/g to 700 m²/g, aparticle diameter in the range from 4 nm to 150 nm, and having apercentage of silica greater than or equal to 5% by weight.

[0009] Under preferred conditions of the above process, a suspension ofbasic anionic colloidal silica containing 5 to 200 parts of silicaexpressed as dry matter is reacted with an aqueous suspension of acidanionic colloidal silica containing 100 parts of silica expressed as drymatter.

[0010] The process according to the present invention makes it possibleto prepare aqueous suspensions of colloidal silica having a neutral pH(between pH 6 and 8), a small particle size (between 4 nm and 150 nm)and having a silica concentration of up to 30% by weight.

[0011] For this reason, the starting basic and acid suspensions ofcolloidal silica used for the implementation of the process abovecontain preferably at least 5%, advantageously at least 10%, notably atleast 15%, particularly at least 20% and more particularly at least 30%by weight of silica.

[0012] The use of an aqueous suspension of basic colloidal silicainstead of a conventional base solution makes it possible to carry outneutralization of an aqueous suspension of acid colloidal silica in aless aggressive and more controlled manner, which is very importantduring the preparation of neutral aqueous suspensions of colloidalsilica on an industrial scale.

[0013] The suspensions of anionic silica having a neutral pH as obtainedby the process according to the present invention exhibit remarkableproperties illustrated below in the experimental part.

[0014] Although composed of small particles and therefore having a highspecific surface, they exhibit excellent stability over time. However,it is known that without a basic pH, this stability over time ofsuspensions of colloidal silica is all the more difficult to obtain ifthe particles of colloidal silica have a high specific surface andtherefore a small particle diameter.

[0015] Their stability over time is equivalent to that of an aqueoussuspension of colloidal silica having a basic pH. This is particularlyremarkable.

[0016] This stability over time is reflected firstly in a constantviscosity of the aqueous suspension of anionic colloidal silica having aneutral pH during storage, and consequently in the absence of theformation of gels or precipitates over time.

[0017] This stability over time is also reflected in a homogeneousdensity of the anionic colloidal suspension having a neutral pH duringstorage, that is, absence of settling over time.

[0018] These properties render the aqueous suspensions of silica thatcan be obtained by the process according to the present inventionparticularly attractive, particularly for the clarification of beer.

[0019] For this reason, the present invention also provides the use ofaqueous suspensions of neutral colloidal silica described above for theclarification of fermented unfiltered beer and also for theclarification of unfermented unfiltered beer.

[0020] More particularly, it provides a process for the clarification offermented unfiltered beer, characterized in that an aqueous suspensionof colloidal silica having a neutral pH as defined above is added to afermented unfiltered beer, flocculation is allowed to take place, thenthe deposit formed is separated and a clear beer having good stabilityand a sodium content equivalent to unrefined beer is obtained.

[0021] The present invention also provides a process for theclarification of the beer above, characterized in that an aqueoussuspension of colloidal silica having a neutral pH is added to afermented unfiltered beer as indicated above, in the presence ofpolyvinyl pyrrolidone.

[0022] The present invention also provides a process for theclarification of fermented unfiltered beer above, characterized in that2 g to 500 g/hectoliter, notably 5 g to 500 g/hectoliter, preferably 20g to 100 g/hectoliter, more particularly 25 g to 75 g/hectoliter andmore specifically 50 g/hectoliter of an aqueous suspension of colloidalsilica having a neutral pH above is added to a fermented unfilteredbeer.

[0023] This suspension was preferably diluted beforehand in 2 to 100parts of water containing 0.1 g to 10 g of CO₂/liter.

[0024] The present invention also provides a process for theclarification of fermented unfiltered beer above, characterized in thatan aqueous suspension of colloidal silica having a neutral pH accordingto the invention is added to a fermented unfiltered beer in the presenceof 5 g to 50 g/hectoliter, preferably 5 g to 10 g/hectoliter and morespecifically about 10 g/hectoliter of polyvinyl pyrrolidone.

[0025] Under preferred conditions of implementing the processes above,the aqueous suspension of colloidal silica having a neutral pH is addedbefore the beer is refined.

[0026] Under other conditions of use, the suspension of colloidal silicahaving a neutral pH is added after the beer has been refined and beforefiltration thereof.

[0027] Surprisingly, and unforeseeable by the person skilled in the art,it has now been found that the use of pH-neutral anionic colloidalsilicon dioxide gives the preparations very good spreadability on theskin and prevents the sticky feel on the skin which often arises.

[0028] A basic prerequisite for the use of this colloidal silicondioxide in preparations with which humans come into contact is acompatible pH. It has hitherto not been possible to incorporatecolloidal silicon dioxide into preparations with a compatible pH sincethe silicon dioxide precipitates out as a result of neutralization.

[0029] Only the possibility of preparing pH-neutral anionic colloidalsilicon dioxide makes such preparations possible.

[0030] U.S. Pat. No. 5,827,508 describes the use of a dibenzoylmethanesunscreen component together with zinc oxide for protecting against UVradiation. As is described therein, unprotected exposure of human skinto UV radiation can cause short-term negative effects such as erythema(sunburn), and long-term damage such as producing changes inpigmentation and leading to skin cancer.

[0031] For this purpose, there is a wide supply of sunscreenpreparations for targeted use before and during sunbathing, but,increasingly, also products for daily use against the long-term effectsof solar irradiation.

[0032] One problem here is the often adequate protection against UVBradiation (290 to 320 nm wavelength) but the inadequate protectionagainst UVA radiation (320 to 400 nm wavelength). The use ofdibenzoylmethane sunscreen components, and of other organic UVA filtersand/or of inorganic filters such as zinc oxide brings disadvantages inthis respect.

[0033] A frequent disadvantageous property of sunscreen formulations ispoor spreadability on the skin, and a very sticky feel after use.

[0034] Finally, the present invention also provides the use of theaqueous suspensions of neutral colloidal silica described above for thepreparation of cosmetic creams.

[0035] The preparations according to the present invention are suitablefor protecting human skin, specifically for protecting against thenegative effects of UV radiation. They can be formulated in a broaddiversity of product forms, such as, for example, emulsions, gels,fluids, lotions, creams, sprays, sticks, oils, foams, lipsticks,moisture-impregnated cleansing and care wipes etc.

[0036] The preferred conditions of implementing the processes accordingto the invention also apply to the other subject matter of theinvention, notably to the applications of the suspensions thus obtained.

[0037] The preparations according to the invention comprise between 0.01and 20% by weight, preferably between 0.1 and 10% by weight,particularly preferably between 0.2 and 7% by weight, of pH-neutralcolloidal silicon dioxide in suspension. In order to prevent a whiteningeffect, the particle size of the silicon dioxide is between 4 nm and 150nm, preferably between 4 nm and 50 nm.

[0038] The preparations according to the invention can comprise one ormore further components which can scatter, reflect or absorb UVradiation. The preparation displays a synergistically higher UVabsorption than the individual components on their own.

[0039] Suitable for this purpose are, inter alia: 2-ethylhexylp-methoxycinnamate, ethylhexyl salicylate, octocrylene,oxybenzone/benzophenone-3, benzophenone-4, benzophenone-5, ethylhexylN,N-dimethylaminobenzoate, 4-aminobenzoic acid/PABA, ethylhexyl dimethylPABA, phenylbenzimidazole-sulphonic acid, homomenthyl salicylate,homosalate, isoamyl methoxy-cinnamate, 4-methylbenzylidenecamphor,3-benzylidenecamphor,benzene-1,4[bis(3-methylidenecamphor-methylsulphonic)]acid, camphorbenzalkonium methosulphate, phenylbenzimidazolesulphonic acid,terephthalylidene dicamphorsulphonic acid, butylmethoxydibenzoylmethane,benzylidene-camphorsulphonic acid,polyacrylamidomethylbenzylidenecamphor, PEG-25PABA, ethylhexyltriazone,drometrizole trisiloxane,methylenebis-benzo-triazolyltetramethylbutylphenol,dioctylbutamidotriazone, disodium phenyl dibenzimidazoletetrasulphonate, bis-ethylhexyloxyphenol methoxyphenol-triazine,4-isopropylbenzyl salicylate, terephthalylidenedicamphorsulphonic acidand mixtures.

[0040] Pigments/micropigments which can be of use are surface-treated oruntreated titanium dioxide, iron oxide and/or zinc oxide and mixturesthereof.

[0041] As further auxiliaries and additives, the preparations accordingto the invention can comprise self-tanning agents, emulsifiers,thickeners, superfatting agents, fats, waxes, stabilizers, biogenicactive ingredients, antioxidants, hydrotropes, solubilizers, bodyingagents, surfactants, cationic polymers, glycerol, preservatives,dispersants, and also protein derivatives, such as gelatins, collagenhydrolysates, natural or synthetic-based polypeptides, egg yolk,lecithin, lanolin and lanolin derivates, fatty alcohols, silicones,deodorizing agents, substances with keratolytic and keratoplasticaction, enzymes and carrier substances, and moisturizing substances,dyes and fragrances. Furthermore, agents with antimicrobial action canbe added to the preparations according to the invention.

[0042] Self-tanning agents which can be used are dihydroxyacetones.

[0043] Anionic emulsifiers which may be used are: C₁₀-C₂₀-alkyl andalkylene carboxylates, alkyl ether carboxylates, fatty alcoholsulphates, fatty alcohol ether sulphates, alkylamide sulphates andsulphonates, fatty acid alkylamide polyglycol ether sulphates, alkanesulphates, alkanesulphonates and hydroxyalkanesulphonates,olefinsulphonates, acyl esters of isethionates, sulphofatty acid esters,alkylbenzenesulphonates, alkylphenol glycol ether sulphonates,sulphosuccinates, sulphosuccinic monoesters and diesters, fatty alcoholether phosphates, protein fatty acid condensation products,alkylmonoglyceride sulphates and sulphonates, alkylglyceride ethersulphonates, fatty acid methyltaurides, fatty acid sarcosinates,sulphoricinoleates, amphoacetates or amphoglycinates, acyl glutamates.These compounds and mixtures thereof are used in the form of theirwater-soluble or water-dispersible salts, for example the sodium,potassium, magnesium, ammonium, mono-, di- and triethanolammonium saltsand analogous alkylammonium salts.

[0044] Suitable cationic emulsifiers are quaternary ammonium salts suchas di-(C₁₀-C₂₄-alkyl)dimethylammonium chloride or bromide, preferablydi-(C₁₂-C₁₈-alkyl)-dimethyl-ammonium chloride or bromide;C₁₀-C₂₄-alkyldimethylethyl-ammonium chloride or bromide;C₁₀-C₂₄-alkyltrimethylammonium chloride or bromide, preferablycetyltrimethylammonium chloride or bromide andC₂₀-C₂₂-alkyltrimethylammonium chloride or bromide;C₁₀-C₂₄-alkyldimethylbenzyl-ammonium chloride or bromide, preferablyC₁₂-C₁₈-alkyldimethylbenzyl-ammonium chloride;N-(C₁₀-C₁₈-alkyl)-pyridinium chloride or bromide, preferablyN-(C₁₂-C₁₆-alkyl)pyridinium chloride or bromide;N-(C₁₀-C₁₈-alkyl)isoquinolinium chloride, bromide or monoalkyl sulphate;N-(C₁₂-C₁₈-alkylpolyoylaminoformylmethyl)pyridinium chloride;N-(C₁₂-C₁₈-alkyl)-N-methylmorpholinium chloride, bromide or monoalkylsulphate; N-(C₁₂-C₁₈-alkyl)-N-ethylmorpholinium chloride, bromide ormonoalkyl sulphate; C₁₆-C₁₈-alkylpentaoxethylammonium chloridediisobutylphenoxyethoxyethyl-dimethylbenzylammonium chloride; salts ofN,N-diethylaminoethylstearylamide and -oleylamide with hydrochloricacid, acetic acid, lactic acid, citric acid, phosphoric acid,N-acylaminoethyl-N,N-diethyl-N-methylammonium chloride, bromide ormonoalkyl sulphate and N-acylaminoethyl-N,N-diethyl-N-benzylammoniumchloride, bromide or monoalkyl sulphate, where acyl is preferablystearyl or oleyl.

[0045] Examples of suitable nonionic emulsifiers which can be used ashydrophilic component are fatty alcohol ethoxylates (alkylpolyethyleneglycols); alkylphenol polyethylene glycols; alkylmercaptan polyethyleneglycols; fatty amine ethoxylates (alkylaminopolyethylene glycols); fattyacid ethoxylates (acylpolyethylene glycols); polypropylene glycolethoxylates (poloxoamers); fatty acid amide polyethylene glycols;N-alkyl-, N-alkoxypolyhydroxy fatty acid amide, in particular fatty acidN-methylglucamides, sucrose esters; polyglycol ethers, alkylpolyglycosides, phosphoric esters (mono-, di- and triphosphoric estersethoxylated and non-ethoxylated), amine oxides, e.g.C₁₂-C₁₈-alkyldimethylamine oxide, fatty acid amidoalkyldimethylamineoxide.

[0046] Amphoteric emulsifers are: N-(C₁₂-C₁₈-alkyl)-∃-aminopropionatesand N-(C₁₂-C₁₈-alkyl)-∃-iminodipropionates as alkali metal and mono-,di- and trialkylammonium salts; N-acylaminoalkyl-N,N-dimethylacetobetaine, preferably N-(C₈-C₁₈-acyl)aminopropyl-N,N-dimethylacetobetaine; C₁₂-C₁₈-alkyldimethylsulphopropylbetaine;amphoteric surfactants based on imidazoline (trade name: Miranol®,Steinapon®), preferably the sodium salt of1-(carboxymethyloxyethyl)-1-(carboxymethyl)-2-laurylimidazolinium andacyl glutamate.

[0047] Suitable non-ionogenic O/W co-emulsifiers are addition productsof from 2 to 30 mol of ethylene oxide and/or 0 to 5 mol of propyleneoxide with linear fatty alcohols having 8 to 22 carbon atoms, with fattyacids having 12 to 22 C atoms and with alkylphenols having 8 to 15 Catoms in the alkyl group; C₁₂-C₁₈ fatty acid mono- and diesters ofaddition products of from 1 to 30 mol of ethylene oxide with glycerol;glycerol mono- and diesters and sorbitan mono- and diesters of saturatedand unsaturated fatty acids having 6 to 22 carbon atoms and the ethyleneoxide addition products thereof; addition products of from 15 to 60 molof ethylene oxide with castor oil and/or hydrogenated castor oil; polyoland, in particular, polyglycerol esters, such as, for example,polyglycerol polyricinoleate and polyglycerol poly-12-hydroxystearate.Also suitable are mixtures of compounds from two or more of theseclasses of substance. The addition products of ethylene oxide and/orpropylene oxide with fatty alcohols, fatty acids, alkylphenols, glycerolmono- and diesters, and sorbitan mono- and diesters of fatty acids orwith castor oil are known, commercially available products. These arehomologue mixtures whose average degree of alkoxylation corresponds tothe ratio of the amounts of ethylene oxide and/or propylene oxide andsubstrate with which the addition reaction is carried out.

[0048] Likewise suitable as hydrophilic component are the polymersreferred to as “soil release polymers” in particular oligoestersobtained by polycondensation of from 40 to 52, preferably 45 to 50 mol %of one or more dicarboxylic acids or esters thereof, 10 to 40,preferably 20 to 35 mol % of ethylene glycol and/or propylene glycol, 3to 20, preferably 10 to 15 mol % of polyethylene glycol, 0 to 10 mol %of a water-soluble addition product of from 5 to 80 mol of an alkyleneoxide with 1 mol of C₁-C₂₄-alcohols, C₆-C₁₈-alkylphenols orC₈-C₂₄-alkylamines and 0 to 10 mol % of one or more polyols having 3 to6 hydroxyl groups.

[0049] Examples of suitable oily substances are Guerbet alcohols having6 to 18, preferably 8 to 10 carbon atoms, esters of linear C₆-C₁₃-fattyacids with linear C₆-C₂₀-fatty alcohols, esters of branchedC₆-C₁₃-carboxylic acids with linear C₆-C₂₀-fatty alcohols, esters oflinear C₆-C₁₈-fatty acids with branched alcohols, in particular2-ethylhexanol, esters of linear and/or branched fatty acids withpolyhydric alcohols (such as, for example, dimerdiol or trimerdiol)and/or Guerbet alcohols, triglycerides based on C₆-C₁₀-fatty acids,vegetable oils, branched primary alcohols, substituted cyclohexanes,Guerbet carbonates, dialkyl ethers, aliphatic or aromatic.

[0050] Examples of substances which can be used as superfatting agentsare polyethoxylated lanolin derivates, lecithin derivates, polyol fattyacid esters, monoglycerides and fatty acid alkanolamides, the latteralso serving as foam stabilizers. Typical examples of fats areglycerides, and suitable waxes are, inter alia, beeswax, paraffin wax ormicrocrystalline waxes, optionally in combination with hydrophilicwaxes, e.g. cetylstearyl alcohol.

[0051] Suitable antioxidants are superoxide dismutase, tocopherol(vitamin E) and ascorbic acid (vitamin C).

[0052] Particularly suitable thickeners and dispersants are ethyleneglycol esters of fatty acids having 14 to 22, particularly preferably 16to 22 carbon atoms, in particular mono- and diethylene glycol stearate.Also preferred are stearin monoethanolamide, stearin diethanolamide,stearin isopropanolamide, stearin monoethanolamide stearate, stearylstearate, cetyl palmitate, glyceryl stearate, stearamide diethanolamidedistearate, stearamide monoethanolamide stearate, N,N-dihydrocarbyl(C₁₂-C₂₂, in particular C₁₆-C₁₈)-amidobenzoic acid and soluble saltsthereof, N,N-di(C₁₆-C₁₈)amidobenzoic acid and derivates. Particularlysuitable are polyacrylates, carbomers, in particular water-soluble orwater-swellable copolymers based on acrylamidoalkylsulphonic acids andN-vinylcarboxamides.

[0053] In principle, suitable solubilizers are all mono- or polyhydricalcohols and ethoxylated alcohols. Preference is given to using alcoholshaving 1 to 4 carbon atoms, such as ethanol, propanol, isopropanol,n-butanol and isobutanol, glycerol and mixtures of said alcohols.Further preferred alcohols are polyethylene glycols having a relativemolecular mass below 2000. Particular preference is given to the use ofpolyethylene glycol having a relative molecular mass between 200 and 600and in amounts up to 45% by weight and of polyethylene glycol having arelative molecular mass between 400 and 600 in amounts of from 0.5 to15% by weight. Further suitable solvents are, for example, triacetin(glycerol triacetate) and 1-methoxy-2-propanol.

[0054] Suitable carrier materials are vegetable oils, natural andhydrogenated oils, waxes, fats, water, alcohols, polyols, glycerol,glycerides, liquid paraffins, liquid fatty alcohols, sterol,polyethylene glycols, cellulose and cellulose derivates.

[0055] Fungicidal active ingredients which may be used are ketoconazole,oxiconazole, terbinafine, bifonazole, butoconazole, cloconazole,clotrimazole, econazole, enilconazole, fenticonazole, isoconazole,miconazole, sulconazole, tioconazole, fluconazole, itraconazole,terconazole, naftifine, Zn pyrethione and octopirox.

[0056] Care substances which can be used are allantoin and bisabolol inthe amounts of 0.0001 to 10% by weight.

[0057] Suitable cationic polymers are, for example, cationic cellulosederivates, cationic starch, copolymers of diallylammonium salts andacrylamides, quaternized vinylpyrrolidone/vinylimidazole polymers,condensation products of polyglycols and amines, quaternized collagenpolypeptides, quaternized wheat polypeptides, polyethyleneimines,cationic silicone polymers such as, for example, amidomethicones,copolymers of adipic acid anddimethylamino-hydroxypropyldiethylenetriamine, polyaminopolyamide,cationic chitin derivates such as, for example, chitosan.

[0058] Examples of suitable silicone compounds are dimethylpolysiloxane,methylphenylpolysiloxanes, cyclic silicone and amino-, fatty acid-,alcohol-, polyether-, epoxy-, fluorine- and/or alkyl-modified siliconecompounds, and polyalkylsiloxanes, polyalkylarylsiloxanes, polyethersiloxane copolymers, as described in U.S. Pat. No. 5,104,645 andpublications cited therein, which may either be liquid or else in resinform at room temperature.

[0059] The preparations according to the invention can be mixed withconventional ceramides, pseudoceramides, fatty acidN-alkylpolyhydroxyalkylamides, cholesterol, cholesterol fatty acidesters, fatty acids, triglycerides, cerebrosides, phospholipids andsimilar substances.

[0060] Examples of available moisturizing substances are isopropylpalmitate, glycerol and/ or sorbitol, which can be used in amounts of0.1 to 50% by weight.

[0061] The total amount of auxiliaries and additives can be 1 to 10,preferably 2 to 5% by weight, based on the composition.

[0062] Another objekt of the present invention is the use of the aqueoussuspensions of neutral colloidal silica described above for thepreparation of ink for ink jet printing.

[0063] A further objekt of the present invention is the the use of theaqueous suspensions of neutral colloidal silica described above forpaints and anticorrosive treatments.

[0064] The examples below illustrate the invention.

EXAMPLE 1

[0065] Preparation of an Aqueous Suspension of Colloidal Silica (A)Having a pH of 7.0 and a Mean Particle Diameter of 9 nm

[0066] An aqueous suspension of colloidal silica (B) having a pH of 9,containing 30 wt. % of silica, mean particle diameter 9 nm, andstabilized with sodium was deionised by being passed over a cationexchange resin containing sulfonic groups in the acid form.

[0067] An aqueous suspension of colloidal silica (C) having a pH of 2.2and containing 30 wt. % of silica, mean particle diameter 9 nm, wasobtained. This suspension (C) was very unstable and therefore had to beused very quickly.

[0068] 30.5 g of the aqueous suspension of basic colloidal silica (B)was then added, with stirring, to 145.1 g of the aqueous suspension ofacid colloidal silica (C).

[0069] The aqueous suspension of neutral colloidal silica (A) obtainedhad the following characteristics:

[0070] pH: 7.0

[0071] density: 1.200

[0072] % titratable Na₂O: 0.095%

[0073] % total Na₂O: 0.19%

[0074] specific surface: 280 m²/g

[0075] mean particle diameter: 9 nm

[0076] % of silica: 30 wt. %.

[0077] The storage stability of this aqueous suspension of neutralcolloidal silica (A) was comparable with that of an aqueous suspensionof basic colloidal silica of type (B). Storage Neutral suspensionstability A Basic suspension B Acid suspension C 25° C. >6 months >6months 24 hours 50° C. >6 months >6 months 10 hours 75° C. >6 months >6months  1 hour

EXAMPLE 2

[0078] Preparation of an Aqueous Suspension of Colloidal Silica (D)Having a pH of 7.0, Mean Particle Diameter 12 nm

[0079] An aqueous suspension of colloidal silica (E) having a pH of 9,containing 30 wt. % of silica, mean particle diameter 12 nm, andstabilized with potassium was deionised by being passed over a cationexchange resin containing sulfonic groups in the acid form. An aqueoussuspension of colloidal silica (F) having a pH of 2.3 containing 30 wt.% of silica, mean particle diameter 12 nm, was obtained. This suspension(F), which was very unstable, therefore had to be used rapidly.

[0080] 45 g of the aqueous suspension of basic colloidal silica E werethen added, with stirring, to 150 g of the aqueous suspension of acidcolloidal silica F. An aqueous suspension of neutral colloidal silica(D) was obtained, the characteristics of which were as follows:

[0081] pH: 7.0

[0082] density: 1.202

[0083] % titratable K₂O: 0.3%

[0084] specific surface: 200 m²/g

[0085] mean particle diameter: 12 nm

[0086] % of silica: 30 wt. %.

[0087] The storage stability of this aqueous suspension of neutralcolloidal silica (D) was tested and it was comparable with the stabilityof a suspension of basic colloidal silica of type (E). Storage Neutralsuspension stability D Basic suspension E Acid suspension F 25° C. >6months >6 months 8 hours 50° C. >6 months >6 months 1 day 75° C. >6months >6 months 4 hours

EXAMPLE 3

[0088] Preparation of an Aqueous Suspension of Colloidal Silica (G)Having a pH of 7.0. Mean Particle Diameter 25 nm

[0089] A basic aqueous suspension of colloidal silica (H) having a pH of9, containing 30 wt. % of silica, mean particle diameter 25 nm, andstabilized with sodium was deionised by being passed over a cationexchange resin containing sulfonic groups in the acid form.

[0090] An acid aqueous suspension of colloidal silica (I) having a pH of2.3 containing 30 wt. % of silica, mean particle diameter 25 nm, wasobtained. This suspension (I), which was very unstable, therefore had tobe used rapidly.

[0091] 51 g of the basic aqueous suspension of colloidal silica (H) werethen added, with stirring, to 68.5 g of the acid aqueous suspension ofcolloidal silica (I).

[0092] An aqueous suspension of neutral colloidal silica (G) was thenobtained, the characteristics of which were as follows:

[0093] pH: 7.0

[0094] density: 1.197

[0095] titratable Na₂O: 0.3%

[0096] specific surface: 115 m²/g

[0097] mean particle diameter: 25 nm

[0098] % of silica: 30 wt. %.

[0099] The storage stability of this suspension of neutral colloidalsilica (G) was tested and it was comparable with the stability of asuspension of basic colloidal silica of type (H). Storage stabilityNeutral suspension G Basic suspension H 25° C. >6 months >6 months 50°C. >6 months >6 months 75° C. >6 months >6 months

COMPARISON EXAMPLE 1

[0100] Preparation of an Aqueous Suspension of Colloidal Silica (A′)Having a pH of 7, Mean Particle Diameter: 9 nm, Stabilized with Sodium

[0101] 15 g of 1N sulfuric acid were added, with stirring, to 100 g ofthe basic aqueous suspension (B) described in Example 1, to obtain a pHof 7.

[0102] An aqueous suspension of neutral colloidal silica (A′) wasobtained, having the following storage stability characteristics:Storage stability Neutral suspension A′ Basic suspension B 25° C. 2 h >6months 50° C. 20 minutes >6 months 75° C. rapid gelling >6 months

[0103] It was observed that the aqueous suspension of neutral colloidalsilica (A′) obtained by neutralization, by an acid, of an aqueoussuspension of basic colloidal silica (B) cannot be used commerciallybecause of its very poor stability.

EXAMPLE 4

[0104] Use of the Aqueous Suspension of Neutral Colloidal Silica (A) forClarification of Fermented Unfiltered Beer

[0105] 50 g/hectoliter or 100 g/hectoliter of an aqueous suspension ofneutral colloidal silica (A) as described in Example 1 were added tounrefined beer (J) which had undergone a principal fermentation of 7days at 8° C.

[0106] This beer, to which the aqueous suspension of neutral colloidalsilica (A) had been added, was stored in a tank for 4 weeks at 3° C.

[0107] Filtration was then carried out over a kieselguhr filter. Thefiltered samples were then casked by the brewery to ensure that theinfluence of oxygen was minimized for the Forcing test.

[0108] The stability of the beer was measured by the Forcing test (0 °C./40° C./0° C.), the foam was tested by the Ross and Clark test, andthe color by the European Brewery Convention test (EBC).

[0109] The results obtained are summarized in the table below: Amount ofaqueous suspension of neutral colloidal silica (A) added 0 g/hl 50 g/hl100 g/hl Stability (hot days) 8 ≧25 ≧25 Color (EBC) 4.4 4.4 4.4 Foam 10565 55 pH 4.29 4.36 4.38 Na in mg/l 7.9 8.3 8.1 Ca in mg/l 29.7 30.9 29.9K in mg/l 460 490 477 Mg in mg/l 81.8 85.7 84.5 Tannoid in mg/l 55 52 51Anthocyanogen in mg/l 55 58 55 Flavanoid in mg/l 40 28 30

[0110] It was observed that the addition of 50 g/hl or of 100 g/hl of anaqueous suspension of neutral colloidal silica (A) appreciably improvedthe stability of the beer without a notable modification in the sodium,calcium, potassium and magnesium contents. Moreover, it was observedthat the addition of 50 g/hl or of 100 g/hl of an aqueous suspension ofneutral colloidal silica (A) allowed a good reduction in polyphenols(tannoid, anthocyanogen, flavanoid) present in the beer.

[0111] An added amount of 50 g/hl of an aqueous suspension of neutralcolloidal silica (A) allowed a distinct improvement to be obtained inmost of the desired characteristics in comparison with a beer notcontaining such an aqueous suspension.

EXAMPLE 5

[0112] Use of an Aqueous Suspension of Neutral Colloidal Silica in thePresence of Polyvinyl Pyrrolidone for Clarification of FermentedUnfiltered Beer

[0113] 50 g and 100 g/hectoliter of an aqueous suspension of neutralcolloidal silica (A) as described in Example 1 were added to unrefinedbeer (J) which had undergone a principal fermentation of 7 days at 8° C.

[0114] This beer, to which the aqueous suspension of neutral colloidalsilica (A) had been added, was stored in a tank for 4 weeks at 3° C.

[0115] 10 g /hectoliter of polyvinyl pyrrolidone were added, thenfiltration was carried out over a kieselguhr filter after one hour'scontact.

[0116] The filtered samples were then casked by the brewery to ensurethat the influence of oxygen was minimized for the Forcing test.

[0117] The results obtained are summarized in the table below: 0 g/hl of50 g/hl of 100 g/hl of suspension suspension suspension (A) + 0 g/hl(A) + 10 g/hl (A) + 10 g/hl of poly-vinyl of polyvinyl of poly-vinylpyrrolidone pyrrolidone pyrrolidone Stability (hot days) 11 13 15 Color(EBC) 4.5 4.5 4 Foam 110 95 85 PH 4.25 4.29 4.32 Na in mg/l 7.3 7.5 7.0Ca in mg/l 29.4 29 29.4 K in mg/l 456 455 473 Mg in mg/l 82.4 83.7 85Tannoid in mg/l 36 29 30 Anthocyanogen in mg/l 54 46 53 Flavanoid inmg/l 35 21 31

[0118] Compared with Example 4, the addition of 10 g/hl of polyvinylpyrrolidone to 50 or 100 g/hl of the aqueous suspension of neutralcolloidal silica A allowed a more pronounced reduction in polyphenols(tannoid, anthocyanogen, flavanoid), and a more stable foam whilstretaining a constant sodium, calcium, potassium and magnesium content.

COMPARISON EXAMPLE 2

[0119] Use of an Aqueous Suspension of Basic Colloidal Silica forClarification of Fermented Unfiltered Beer

[0120] 25, 50, 75 and 100 g/hectoliter of a suspension of basiccolloidal silica (B) as described in Example 1 were added to unrefinedbeer (K) which had undergone a principal fermentation of 7 days at 8° C.

[0121] This beer, to which the aqueous suspension of basic colloidalsilica (B) had been added, was stored in a tank for 4 weeks at 3° C.

[0122] Filtration was then carried out over a kieselguhr filter. Thefiltered samples were then casked by the brewery to ensure that theinfluence of oxygen was minimized for the Forcing test.

[0123] The results obtained are summarized in the table below: 0 g/hl of25 g/hl of 50 g/hl of 75 g/hl of suspension suspension suspensionsuspension (B) (B) (B) (B) Stability, hot Days 0.3 2 3 3.5 Color (EBC)2.8 1.9 1.4 1.2 Foam 107 116 122 118 Na in mg/l 5.8 8.1 8.1 8.5 Ca inmg/l 30 27 27 25 Mg in mg/l 100 101 95 90

[0124] It was noted that the addition of an aqueous suspension of abasic colloidal silica (B) to the fermented unfiltered beer increasedthe stability of the latter. On the other hand, a considerable increasein the sodium content of the filtered beer was observed, which is notauthorized by the Rheinheitsgebot (German purity law).

EXAMPLE 6

[0125] After the principal fermentation of seven days at 8° C., 0 to 100g/hL of an aqueous suspension of neutral colloidal silica (A) asdescribed in Example 1 were added to unrefined beer (beer originatingfrom the same batch of malt after 7 days' fermentation at 8° C.).

[0126] This beer, to which the aqueous suspension of neutral colloidalsilica (A) had been added, was stored in a tank for four weeks at 3° C.

[0127] Filtration was then carried out over a kieselguhr filter. Thefiltered samples were then casked by the brewery to ensure that theinfluence of oxygen was minimized for the Forcing test.

[0128] The stability of the beer was measured by means of the Forcingtest (0° C./40° C./0° C.). The foam was evaluated by the Ross and Clarktest.

[0129] The results obtained are summarized in the table below: Addedamount of aqueous suspension of neutral colloidal silica (A) StabilityColor (g/hL) (hot days) (EBC*) Foam pH 0 8 4.4 105 4.29 10 >20 4.4 1024.30 20 >20 4.4 100 4.32 50 >20 4.4 65 4.36 100 >20 4.4 55 4.38

[0130] The addition of small quantities of an aqueous suspension ofneutral colloidal silica (A) allowed a distinct improvement in thestability of the beer without altering the color and foam values.

EXAMPLE 7

[0131] One part of neutral colloidal silica (A) was diluted with 10parts of carbonated water (0.5 g CO₂/L). This dilution had nodestabilizing effect on the neutral colloidal silica (A).

[0132] After the principal fermentation of seven days at 8° C., 0 to 100g/hL of colloidal silica were added to unrefined beer (beer originatingfrom the same batch of malt after 7 days' fermentation at 8° C.).

[0133] This beer, to which neutral colloidal silica (A) had been added,was stored in a tank for four weeks at 3° C. 10 g of PVPP were thenadded and, after one hour, filtration was then carried out over akieselguhr filter. The filtered samples were then casked by the breweryto ensure that the influence of oxygen was minimized for the Forcingtest.

[0134] The stability of the beer was measured by means of the Forcingtest (0° C./40° C./0° C.). The foam was evaluated by the Ross and Clarktest.

[0135] The results obtained show, as in Example 1, an improvement in thestability whilst retaining a low sodium content and without altering thecolor, calcium, potassium and magnesium values.

EXAMPLE8

[0136] One part of neutral colloidal silica (A) was diluted with 100parts of carbonated water (0.5 g CO₂/L).

[0137] After the principal fermentation of seven days at 8° C., 0 to 100g/hL of neutral colloidal silica (A) were added to unrefined beer (beeroriginating from the same batch of malt after 7 days' fermentation at 8°C.).

[0138] This beer, to which neutral colloidal silica (A) had been added,was stored in a tank for four weeks at 3° C. 10 g of PVPP were thenadded and, after one hour, filtration was then carried out over akieselguhr filter. The filtered samples were then casked by the breweryto ensure that the influence of oxygen was minimized for the Forcingtest.

[0139] The stability of the beer was measured by means of the Forcingtest (0° C./40° C./0° C.). The foam was evaluated by the Ross and Clarktest.

[0140] The results obtained show, as in Example 1, an improvement in thestability whilst retaining a low sodium content and without altering thecolor, calcium, potassium and magnesium values.

EXAMPLE 9

[0141] Use of an aqueous suspension of neutral colloidal silica for theproduction of an oil in water sunscreen cream

[0142] 1) The following constituents were mixed at 80° C.:

[0143] 5% ®Hostaphat CS120 Clariant (stearyl phosphate)

[0144] 2.5% ®Tegin M (glyceryl stearate)

[0145] 2% stearic acid

[0146] 1% cetyl alcohol

[0147] 2% Abil 100 (dimethicone)

[0148] 3% low viscosity mineral oil

[0149] 3% ®Cetiol 868 (octyl stearate)

[0150] 3% Myritol 318 (caprylic/capric triglyceride)

[0151] 5% ®Eusolex 6300 (camphor-4-methylene xylidene)

[0152] 2) The following were then added:

[0153] 0.2% ®Pemulen TR1 (crosslinked polymer acrylates/C₁₀₋₃₀-alkylacrylate)

[0154] 12.5% of aqueous suspension of neutral colloidal silica (A)

[0155] 3) The constituents of part 1) were homogenized in part 2).

[0156] 4) The following constituents were heated to 80° C.:

[0157] 0.6% ®Hostapon CL g (sodium lauroyl glutamate)

[0158] 4% ®Eusolex 232 (phenylbenzimidazone sulfonic acid)

[0159] 2.21% tromethamine (tris(hydroxymethylol) aminomethane)

[0160] 0.2% allantoin Clariant

[0161] 5% glycerol

[0162] preservative: 90

[0163] Water: 49.49%

[0164] Perfume: 0.30%

[0165] 5) Part 4) was introduced into part 3) at 35° C.

[0166] 6) The emulsion was homogenized.

[0167] The sunscreen cream obtained made it possible to avoid thewhiteness brought about by titanium dioxide and gave a softer and morepleasant sensation when applied to the skin.

[0168] The examples below aim to illustrate the subject-matter of theinvention in more detail, without limiting it thereto. In the table, %means % by weight.

EXAMPLE 10

[0169] Day Cream with UV Protection INCI Trade name (Example) % MineralOil Paraffin oil low-viscosity 7 Isopropyl Palmitate Tegosoft P,Crodamol IPP 6 Glyceryl Stearate Tegin M, Cutina GMS 0.5 CetearylAlcohol Lanette O 0.5 Capric/Caprylic Triglyceride Myritol 318 2Benzophenone-3 Neo Heliopan BB, Eusolex 4360 1 MethyleneBis-Benzotriazolyl Tinosorb M 3 Tetramethylbutylphenol Silica neutralKlebosol 0 to 5 Cetyl Phosphate Hostaphat CC 100 0.5 Caprylyl MethiconeSilCare 41M15 1 Ammonium Aristoflex AVC 1 Acryloyldimethyltaurate/VPCopolymer Tocopheryl Acetate Vitamin E acetate 1 Sodium Cocoyl GlutamateHostapon CCG 1 Water Water Ad 100 Glycerol Glycerol 5 CitricAcid/Trisodium Citrate Citric acid/citrate buffer q.s.

EXAMPLE 11

[0170] Use of an aqueous suspension of neutral colloidal silica for thepreparation of inks for ink jet printing

EXAMPLE 11′

[0171] 5% of an aqueous suspension of neutral colloidal silica (A) asdescribed in Example 1 was added to a Hostafine Black T ink (80 parts ofwater/20 parts of diethylene glycol). After mixing, filtration wascarried out over a 1 μm filter.

EXAMPLE 11″

[0172] 2.5% of an aqueous suspension of neutral colloidal silica (A) asdescribed in Example 1 was added to a Duasyn Acid Yellow XX-SF ink (80parts of water/20 parts of diethylene glycol).

[0173] After mixing, filtration was carried out over a 0.45 μm filter.

[0174] The physical/chemical characteristics of the inks obtained inExamples 11′ and 11″ are summarized in the table below.

[0175] The printing tests were carried out on a Hewlett Packard 420printer and evaluated visually: Surface tension Viscosity pH (mN/m)(mPas) Hostafine Black T 7.7 42.0 4.337 Hostafine Black T + 5% 7.8 40.63.294 neutral colloidal silica (A) Duasyn Acid Yellow XX-SF 4.0 62.02.442 Duasyn Acid Yellow XX-SF + 2.5% 5.8 59.5 2.261 neutral colloidalsilica (A)

[0176] The addition of small quantities of neutral colloidal silica (A)made it possible to reduce the viscosity, which is advantageous for inksfor ink jet printing.

[0177] Moreover, the printing obtained with the inks of Examples 11′ and11″ was faultless.

1. A process for the preparation of an aqueous suspension of anioniccolloidal silica having a neutral pH, which is stable over time andcomprising individualized particles of colloidal silica which are notbound to one another by siloxane bonds, characterized in that an aqueoussuspension of anionic colloidal silica comprising individualizedparticles of colloidal silica which are not bound to one another bysiloxane bonds and having a basic pH is mixed with an aqueous suspensionof anionic colloidal silica comprising individualized particles ofcolloidal silica which are not bound to one another by siloxane bondsand having an acid pH.
 2. A process according to claim 1, characterizedin that an aqueous suspension of anionic colloidal silica having aneutral pH in the range from 8.5 to 11, a specific surface in the rangefrom 20 m²/g to 700 m²/g, a particle diameter in the range from 4 nm to150 nm and having a percentage of active material of ≧5% by weight, isreacted with an aqueous suspension of anionic colloidal silica having apH in the range from 2 to 3.5, a specific surface in the range from 20m²/g to 700 m²/g, a particle diameter in the range from 4 nm to 150 nmand having a percentage of active material of ≧5% by weight.
 3. Aprocess according to claim 1 or 2, characterized in that an aqueoussuspension of anionic colloidal silica having a pH in the range from 8.5to 11 and containing 5 to 200 parts of silica expressed as dry matter isreacted with an aqueous suspension of anionic colloidal silica having apH in the range from 2 to 3.5 and containing 100 parts of silicaexpressed as dry matter, or vice versa.
 4. The use of an aqueoussuspension of neutral colloidal silica obtained by the process asdefined in any one of claims 1 to 3 for the clarification of fermentedunfiltered beer.
 5. The use of an aqueous suspension of neutralcolloidal silica obtained by the process as defined in any one of claims1 to 3 for the clarification of unfermented unfiltered beer.
 6. Aprocess for the clarification of fermented unfiltered beer according toclaim 4, characterized in that an aqueous suspension of colloidal silicahaving a neutral pH obtained by the process as defined in one of claims1 to 3 is added to a fermented unfiltered beer, flocculation is allowedto take place, then the deposit formed is separated and a clear beer isobtained having good stability and a sodium content equivalent tounrefined beer.
 7. A process according to claim 6, characterized in thatan aqueous suspension of colloidal silica having a neutral pH obtainedby the process as defined in one of claims 1 to 3 is added to afermented unfiltered beer in the presence of polyvinyl pyrrolidone.
 8. Aprocess according to claim 6, characterized in that 5 to 500g/hectoliter of an aqueous suspension of a colloidal silica having aneutral pH obtained by the process as defined in one of claims 1 to 3are added to a fermented unfiltered beer.
 9. A process according toclaim 7, characterized in that an aqueous suspension of colloidal silicahaving a neutral pH obtained by the process as defined in one of claims1 to 3 is added to a fermented unfiltered beer in the presence of 5 to50 g/hectoliter of polyvinyl pyrrolidone.
 10. A process according toclaim 6, characterized in that the aqueous suspension of colloidalsilica having a neutral pH is added before the beer is refined.
 11. Aprocess for the clarification of fermented unfiltered beer according toclaim 6, characterized in that the suspension of colloidal silica havinga neutral pH is added after the beer has been refined and beforefiltration of the latter.
 12. A process according to claim 6,characterized in that 2 to 500 g/hectoliter of an aqueous suspensionwhich was previously diluted in 2 to 100 parts of water containing 0.1 gto 10 g of CO₂/l are added to the fermented unfiltered beer.
 13. The useof an aqueous suspension of anionic colloidal silica having a neutral pHobtained by the process as defined in any one of claims 1 to 3 for thepreparation of cosmetic creams and for the production of preparationsfor protecting the human skin against UV radiation.
 14. Preparation forprotecting the human skin, in particular against UV radiation,comprising an aqueous suspension of anionic colloidal silica having aneutral pH obtained by the process as defined in any one of claims 1 to3.
 15. Preparation according to claim 14, comprising at least onefurther component which can scatter, reflect or absorb UV radiation. 16.Preparation according to claim 14 or 15, comprising, as furthercomponent, 2-ethylhexyl p-methoxycinnamate, ethylhexyl salicylate,octocrylene, oxybenzone/benzophenone-3, benzophenone-4, benzophenone-5,ethylhexyl N,N-dimethylaminobenzoate, 4-aminobenzoic acid/PABA,ethylhexyl dimethyl PABA, phenylbenzimidazolesulphonic acid, homomenthylsalicylate, homosalate, isoamyl methoxycinnamate,4-methylbenzylidenecamphor, 3-benzylidenecamphor,benzene-1,4[bis(3-methylidenecamphormethyl-sulphonic)]acid, camphorbenzalkonium methosulphate, phenylbenzimidazole-sulphonic acid,terephthalylidene dicamphor-sulphonic acid,butylmethoxydibenzoylmethane, benzylidenecamphorsulphonic acid,polyacrylamidomethylbenzylidenecamphor, PEG-25 PABA, ethylhexyltriazone,drometrizole trisiloxane,methylenebis-benzotriazolyltetramethylbutylphenol,dioctylbutamidotriazone, disodium phenyl dibenzimidazoletetrasulphonate, bis-ethylhexyloxyphenol methoxyphenoltriazine,4-isopropylbenzyl salicylate, terephthalylidenedicamphorsulphonic acid,surface-treated or untreated titanium dioxide, surface-treated oruntreated iron oxide, surface-treated or untreated zinc oxide andmixtures thereof.
 17. The use of an aqueous suspension of colloidalsilica having a neutral pH obtained by the process as defined in any oneof claims 1 to 3 for the preparation of ink for ink jet printing. 18.The use of an aqueous suspension of colloidal silica having a neutral pHobtained by the process as defined in any one of claims 1 to 3 forpaints and anticorrosive treatments.